1. Field of the Invention
The present invention relates to a remaining-amount-of-battery detecting device for detecting the remaining amount of battery power.
2. Description of the Related Art
Apparatus of the type using batteries as power sources have conventionally utilized various methods for detecting the remaining amount of battery power. Typical examples are a method of monitoring the discharge voltage of a battery and a method of estimating the remaining amount of battery power by integrating the discharge time of a battery which is fully charged and cumulatively calculating the amount of consumed power. In the case of a charger, a method of monitoring variations of charging voltage is proposed.
However, any of the above-described conventional methods has a number of disadvantages. For example, although each of the methods utilizes the terminal voltage of a battery to detect the remaining amount of battery power, the terminal voltages of individual batteries exhibit large variations, with the result that it is extremely difficult to quantitatively detect the extent of charge or discharge of a battery to be measured, i.e., the remaining amount of battery power or the amount of battery power used, on the basis of the terminal voltage of the battery. It is also extremely difficult to quantitatively display the detected result as the amount of time. For this reason, in any of the conventional methods, the presence or absence of the remaining amount of battery power can only be detected. Additional disadvantage of the conventional method is that, in a case where a battery is charged through a charger, it is impossible to quantitatively detect to what extent the battery has been charged. As a result, it is only possible to know whether the battery is fully charged.
In addition, the method of detecting the remaining amount of battery power by integrating the discharge time and/or discharge current of a battery has limitations in that it is necessary to prepare a battery which is fully charged at the beginning of service and starts integrating the discharge time of the battery in the state of full charge. As a result, this method cannot be applied to an insufficiently charged battery. Also, none of the above-described methods can be adapted to unexpected variations in the service conditions of a battery, and a value detected in such a case is unreliable.
During the operation of a portable apparatus using a battery as a power source, particularly an apparatus whose power consumption is large compared to the capacity of a battery incorporated therein, for example, a portable video camera, since the consumption of the battery rapidly proceeds, an operator will be very anxious for the remaining serviceable time of the apparatus.
As is known, a conventional portable video camera is provided with a remaining-amount-of-battery display for displaying the remaining amount of battery power. The conventional remaining-amount-of-battery display is arranged to measure the output voltage of a battery and give a warning when the measured value falls below a predetermined value.
However, since this method does not allow for the discharge characteristic or internal resistance of a battery, the display accuracy of the remaining amount of battery power has been insufficient. For example, if the output voltages of batteries in a loaded state are the same but their kinds are different from each other, they will exhibit different discharge characteristics. This leads to the problem that a displayed remaining-amount value does not indicate the accurate remaining amount of battery power.
As a remaining-amount-of-battery display of this kind, a certain device is known. This device is arranged to integrate the amount of consumed power corresponding to the state of service of a battery with respect to service time and subtract the integral from the amount of battery power obtainable in a fully charged state, thereby estimating the remaining amount of battery power.
FIG. 1 shows an example of an arrangement in which the remaining-amount-of-battery display is applied to a camera-integrated video tape recorder (or camcorder). The camcorder shown in FIG. 1 comprises a camera unit 1 a VTR unit 2, a battery 4 for supplying electrical power to the camera unit 1 and the VTR unit 2, a system control circuit 5 for controlling the operations of the camera unit 1 and the VTR unit 2, an instructing unit 6 operated to input an instruction indicative of a predetermined operation into the system control circuit 5, a display unit 7 for displaying the state of operation of the system control circuit 5, and a counter 8 for integrating the electrical power consumed by the system. Reference numeral 9 denotes a TV unit for displaying image signals outputted from the camera unit 1 or the VTR unit 2.
When the camcorder shown in FIG. 1 is being used in, for example, a photographing and recording mode, the camera unit 1 and the VTR unit 2 are in operation and the current consumed by the system is 2.4 amperes. In a reproducing mode, if the camera unit 1 is in no operation and only the VTR unit 2 is in operation, the current consumed by the system is 1.8 amperes.
If an operator inputs an instruction indicative of execution of the photographing and recording mode from the instructing unit 6, electrical power is supplied from the battery 4 to the camera unit 1 and/or the VTR unit 2 and each element initiates an operation corresponding to the operating mode specified from the instructing unit 6. During this time, the counter 8 is cumulatively incrementing a count per unit time corresponding to each operating mode.
More specifically, a count factor corresponding to the power consumption required in each operating mode is set in advance, and the system control circuit 5 controls the counting operation of the counter 8 in accordance with each operating mode. In the above-described example, since the consumed currents are 2.4 and 1.8 amperes in the photographing and recording mode and the recording mode, respectively, the corresponding count factors are set to "4" and "3". In the photograping and recording mode, the counter 8 counts up by four per second and, in the reproducing mode, by three per second.
Each time the operation of a main operating unit 3 consisting of the camera unit 1 and the VTR unit 2 is stopped or interrupted, the system control circuit 5 fetches the count of the counter 8, obtains the consumed power of the battery 4 through arithmetic operations, and causes the display unit 7 to display the remaining amount of battery power of the battery 4. When the battery 4 is replaced, the counter 8 is reset.
In the above-described arrangement, the thus-obtained remaining amount of battery power is divided by the value of the current consumed in the photographing and recording mode, whereby the remaining recording time during which photography is possible can be displayed.
However, the arrangement shown in FIG. 1 has a number of disadvantages. For example, if errors in power consumption cumulate which may be produced when the state of operation of the system is switched or due to a difference in fine mode setting, it will be impossible to detect the remaining amount of battery power with high accuracy. It is also impossible to estimate the remaining amount of battery power of a battery which has been halfway consumed. In addition, in a case where an AC power source is used, i.e., in the case of a system which can be used with a so-called AC adapter for transforming AC power into DC power, the arrangement of FIG. 1 operates to integrate the amount of power consumed when the AC adapter is in operation. As a result, the remaining amount of battery power will be inappropriately calculated and displayed.